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Specific short transmembrane sequences can inhibit transformation by the mutant neu growth factor receptor in vitro
F J Lofts1, H C Hurst, M J Sternberg
1Molecular Oncology Laboratory, Hammersmith Hospital, London, UK.
Abstract:
The neu oncogene is activated by a point mutation within its transmembrane domain that results in the substitution of glutamic acid for valine at position 664, and is associated with constitutive activation of the tyrosine kinase. It has been proposed that the mutation allows for stabilization of homodimers of the receptor that are necessary for transduction of the mitogenic signal. To investigate the role of the alpha-helical transmembrane sequence in the function of neu, we constructed an expression vector to produce a variety of short transmembrane neu proteins, lacking ligand binding or intracellular kinase domains. Such sequences should interact with full-length receptors and prevent receptor dimerization and thus act as specific inhibitors of function. These small proteins all included a pentapeptide from position 661-665, which has been proposed to be necessary for packing. We show that the short transmembrane molecules are expressed at the cell surface and can retard the growth of neu-transformed cells in monolayers, as colonies in soft agar and as tumours in animals. As predicted by molecular modelling, the magnitude of inhibition depended on the nature of the packing surface, suggesting that the neu transmembrane domain is directly involved in neu protein dimerization.
Insights
Short neu transmembrane proteins inhibit cancer cell growth by blocking receptor dimerization. This discovery highlights the transmembrane domain's role in neu protein function and offers a potential therapeutic strategy.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- The neu oncogene drives cancer through a mutation in its transmembrane domain, leading to constitutive tyrosine kinase activation.
- This activation is linked to receptor homodimerization, a key step in transmitting growth signals.
Purpose of the Study:
- To investigate the role of the neu transmembrane domain in receptor dimerization and function.
- To develop short transmembrane neu proteins as potential inhibitors of neu-driven cell proliferation.
Main Methods:
- Constructed expression vectors for short transmembrane neu proteins containing a critical pentapeptide.
- Expressed these proteins in cells and assessed their ability to inhibit neu-transformed cell growth in vitro and in vivo.
Main Results:
- Short transmembrane neu proteins were successfully expressed at the cell surface.
- These proteins significantly retarded the growth of neu-transformed cells in monolayers, soft agar colonies, and animal tumors.
- Inhibition correlated with the nature of the transmembrane packing surface, supporting molecular modeling predictions.
Conclusions:
- The neu transmembrane domain directly participates in neu protein dimerization.
- Short transmembrane neu proteins act as specific inhibitors, suggesting a novel therapeutic avenue for neu-amplified cancers.